Field of the Invention
The present invention relates to an image display apparatus and a control method thereof.
Description of the Related Art
There is a technique related to a liquid crystal display apparatus in which a screen is divided into a plurality of divided regions (backlight regions) and the emission brightness of a backlight and the transmittance of a liquid crystal panel are controlled for each divided region (for example, Japanese Patent Application Laid-open No. 2002-99250). With such a technique, for example, the emission brightness of the backlight in a divided region which displays a dark image is set to a low value and the emission brightness of the backlight in a divided region which displays a bright image is set to a high value. In addition, an image signal (transmittance of the liquid crystal panel) is corrected in accordance with the emission brightness of the backlight so that the brightness of an image displayed on a screen is the same between a case where light is emitted from the backlight at a predetermined emission brightness and a case where light is emitted from the backlight at an emission brightness which is based on the brightness of the image. Performing such control enables a misadjusted black level to be suppressed and the contrast to be enhanced.
FIG. 2 shows an example of an image to be displayed. The image shown in FIG. 2 includes a high brightness region (bright portion) with high brightness and a low brightness region (dark portion) with low brightness. With the conventional technique described above, when displaying the image shown in FIG. 2, uneven brightness occurs as shown in FIG. 3. Specifically, in a dark portion around a bright portion, a brightness gradient is created in which the closer a pixel is to the bright portion, the higher the brightness. An image displayed on a screen is shown in an upper half of FIG. 3. The lower half of FIG. 3 shows a brightness distribution on a dashed line A of the image shown in the upper half of FIG. 3. As is apparent from the brightness distribution shown in the lower half of FIG. 3, in a dark portion, a brightness gradient is created even if the emission brightness of the backlight is set to a low level. Such uneven brightness is created when backlight light (light emitted from the backlight) of a divided region is diffused and leaks to the surrounding divided regions. For example, backlight light is diffused by a diffuser plate.
In addition, when controlling the emission brightness for each divided region, the brightness of the backlight (for example, the brightness of light incident to a display panel; backlight brightness) may not always reach the necessary brightness. For example, in a divided region where the emission brightness of the surrounding divided regions is low, since the amount of backlight light that leaks from the surrounding divided regions (leakage light) is small, the backlight brightness may not always reach the necessary brightness. When the brightness of the backlight does not reach the necessary brightness, the reproducibility of the brightness of an image declines. In this case, in order to increase the reproducibility of brightness of an image, the emission brightness of a divided region in which the backlight brightness is insufficient or the emission brightness of the surrounding divided regions can conceivably be increased. However, controlling the emission brightness in this manner causes the brightness gradient described above to become steeper and increases a sense of interference (in other words, the image quality deteriorates).